The 3rd Generation Partnership Project (3GPP) is responsible for the standardization of the UMTS (Universal Mobile Telecommunication Service) system, and LTE is currently under discussion as a next generation mobile communication system of the UMTS system. LTE is a technology for realizing high-speed packet-based communication that can reach high data rates both in the downlink and in the uplink. The 3GPP work on LTE is also referred to as Evolved Universal Terrestrial Access Network (E-UTRAN). Thus work is ongoing in 3GPP to specify an evolution to UTRAN, denoted E-UTRA, as part of the LTE effort. The first release of LTE, referred to as release-8 (Rel-8) can provide peak rates of 300 Mbps, a radio-network delay of e.g. 5 ms or less, a significant increase in spectrum efficiency and a network architecture designed to simplify network operation, reduce cost, etc. In order to support high data rates, LTE allows for a system bandwidth of up to 20 MHz. LTE is also able to operate in different frequency bands and can operate in at least frequency division duplex (FDD) and time division duplex (TDD). Other operation modes can also be used. A radio base station in LTE is known as eNB or eNodeB, which may be viewed as a macro radio base station in LTE.
The subsequence release i.e. LTE release 9 aims to providing further functionalities to support efficiently so called home radio base stations operation and to also to provide a better user experience supporting LTE access technology. These home radio base stations are also known as Home eNBs, HeNBs. The coverage area of a HeNB is smaller than that of a eNB.
For the next generation mobile communications system e.g. IMT-advanced and/or LTE-advanced, which is an evolution of LTE, support for bandwidths of up to 100 MHz is being discussed. One issue with such large bandwidth is that it is challenging to find free 100 MHz of contiguous spectrum, due to that radio spectrum a limited resource. LTE-advanced may be viewed as a release-10 (Rel-10) of the LTE standard and since it is an evolution of LTE, backward compatibility is important so that LTE-advanced can be deployed in spectrum already occupied by LTE (e.g. Rel-8 and/or Rel-9). This means that for a LTE user equipment or a LTE terminal, a LTE-advanced capable network can appear as a LTE network.
The interface between neighbour eNBs is called the X2 interface and X2AP is the X2 application protocol used to convey the signaling between eNBs. Hence, radio network layer signaling procedures of the control plane between eNBs in E-UTRAN transmitted via the X2 interface and X2AP supports the functions of the X2 interface. X2AP is described in 3rd generation partnership project, technical specification 3GPP TS 36.423 entitled: “E-UTRAN, X2 application protocol (X2AP)”.
A plurality of functions may be provided by the X2AP protocol. Examples of functions are: Mobility Management allowing a eNB to move the responsibility of a certain user equipment (UE) to another eNB; Load management used by eNBs to indicate resource status, overload and traffic load to each other; Resetting of the X2 used to reset the X2 interface; Setting up the X2 used to exchange necessary data for the eNB for setup of the X2 interface and implicitly perform an X2 Reset; eNB Configuration Update allowing updating of application level data for two eNBs to interoperate correctly over the X2 interface; Mobility Parameters Management allowing a eNB to coordinate adaptation of mobility parameter settings with a peer eNB; Mobility Robustness Optimization allowing reporting of information related to mobility failure events; Energy Saving. This function allows decreasing energy consumption by enabling indication of cell activation/deactivation over the X2 interface; Mobility Management allowing a eNB to move the responsibility of a certain UE to another eNB, etc. It should be mentioned that a eNB controls at least one cell associated to a cell identifier called “global cell identifier”, and that each eNB belongs to at least one tracking area identified by a code called “tracking area code” which is part of a tracking area identifier. A UE in a serving cell controlled by a serving eNB may move to a new cell controlled by the same eNB or to a new cell controlled by another eNB i.e. a target eNB. For this, a function called automatic neighboring relation (ANR) may be used. The UE reports neighboring cells based on cell measurement data. Based on these measurements, the serving eNB may initiate a new neighbor relation to the target eNB. The ANR function is used in the eNBs. Hence, the UE informs the serving eNB to which it is connected, that it has detected a new neighboring cell controlled by a neighboring eNB i.e. a target eNB. The neighboring eNB may then establish a X2 relation used for e.g. mobility procedures.
In order for two eNBs to interoperate correctly over the X2 interface, a X2 setup procedure may be used to exchange application level information data over the interface. As an example, an initiating eNB may send X2 SETUP REQUEST message to a candidate/target eNB. If possible, the candidate/target eNB replies with the X2 SETUP RESPONSE message. This will establish a relation between the two eNBs. The initiating eNB may transfer, in the SETUP REQUEST message, the complete list of its served cells and, if available, a list of supported Globally Unique (GU) Group Ids to the candidate eNB. The candidate eNB replies with the complete list of its served cells and shall include, if available, a list of supported GU Group Ids in the reply. The SETUP REQUEST message also includes the Global eNB identifier (ID) of the initiating eNB and the SETUP RESPONSE message includes the Global eNB ID of the candidate/target eNB. In general, Global eNB ID is used to globally identify an eNB.
The network topology is however considered too coarse when the global eNB identifiers are used by the eNBs to share information between them. The eNBs may be tracked using derived IP-addresses and neighboring eNB PLMN Id information. But this operation is quite complex in a network topology where there is a huge number of node's relations.